When your furnace is red-tagged, ask a lot of questions

Gayle Zook of Blaine had a 19-year-old furnace until Monday, when it was replaced after being red-tagged on Friday.

Red-tagging, the practice of a heating and air conditioner technician shutting off a furnace because it is unsafe, can occur when a furnace's heat exchanger develops a crack. If wide enough, it can leak deadly carbon monoxide into the home at dangerous levels. Once the furnace is red-tagged, only another furnace contractor can generally "unlock" it, for safety reasons.

Zook spent the weekend with two space heaters that her contractor lent her. "They told me that most furnaces last 13 to 20 years, so mine was due," she said.

But sometimes a red tag is the sign of a scam.

Hearing that odorless-yet-deadly carbon monoxide may be emanating throughout the home can be a scare tactic that will cause consumers to immediately spring $3,000 or more for a new furnace.

"We see a 30 percent uptick during the heating season for scam calls," said Becca Virden, spokeswoman for CenterPoint Energy. "It could be a tagged furnace or someone going door to door saying they're checking for carbon monoxide leaks."

CenterPoint recently joined with other gas and electric utilities across the country and the Better Business Bureau in Utilities United Against Scams to protect consumers from unnecessary red-tagging and other schemes. The Better Business Bureau of Minnesota and North Dakota has logged about 400 complaints in the past three years related to heating and air conditioning contractors applying high-pressure sales techniques as well as overcharging and unsatisfactory work.

To start, they said, homeowners should get a second or even third opinion if a furnace, water heater or gas dryer has been tagged as unsafe. Consumers can ask the contractor to point out the flaw in the exchanger. If it's a hairline crack and the carbon monoxide levels are below 30 part per million, it may be safe but should still be monitored, experts say.

No matter how small, the crack cannot be repaired and will not go away, said Jim San Cartier, manager at Springborn Heating and Air Conditioning in Stillwater. But a heat exchanger can be replaced for about $1,500, half the price of a new furnace. San Cartier also suggests checking to see if the heat exchanger is still under warranty, which can often extend to 20 years. It might buy you extra time before a total furnace replacement.

Also, the contractors and other experts said that homeowners should not let a contractor leave a furnace dismantled. A contractor can shut off the gas line to the furnace without taking it apart or removing major parts. Once dismantled, other companies have a harder time evaluating it.

When hiring an HVAC contractor, choose one that is licensed, bonded and known in the community to minimize a chance of being scammed, the experts said. Bob Cronin, general manager at Action Heating in Spring Lake Park thinks Checkbook.org is a good place to find a qualified source.

"They can't be bought and they have the most reliable scoring system," he said. Checkbook, a nonprofit also known as Twin Cities Consumers' Checkbook, requires a subscription, but its information is free in most libraries.

Furnaces should be tuned up annually or every other year. Generally, the older the furnace the more attention it needs to run as efficiently and safely as possible.

"Err on the side of caution" CenterPoint's Virden said.